Briefly mention the mechanism of action of FSH.

Follicle-stimulating hormone (FSH) is a hormone produced by the anterior pituitary gland that plays a key role in reproductive function, particularly in the regulation of ovarian follicle development and spermatogenesis. The mechanism of action of FSH involves the following steps:

1. Binding to Receptors:

   • FSH binds to specific FSH receptors located on the surface of target cells in the ovaries (granulosa cells) in females and the testes (Sertoli cells) in males.

2. Activation of Signaling Pathways:

   • Upon binding to its receptor, FSH activates intracellular signaling pathways, primarily the cyclic AMP (cAMP) pathway, leading to the activation of protein kinase A (PKA) and other downstream signaling molecules.

3. Granulosa Cell Response (Females):

   • In females, FSH stimulates granulosa cells within ovarian follicles to proliferate and differentiate.
   • FSH promotes the growth and development of ovarian follicles, leading to follicular maturation and the production of estrogen.
   • FSH also induces the expression of receptors for luteinizing hormone (LH) on granulosa cells, priming them for the LH surge that triggers ovulation.

4. Sertoli Cell Response (Males):

   • In males, FSH stimulates Sertoli cells within the seminiferous tubules of the testes.
   • FSH promotes the proliferation and maturation of Sertoli cells, which provide structural support and nourishment to developing sperm cells (spermatogenesis).
   • FSH also stimulates the production of androgen-binding protein (ABP) by Sertoli cells, which helps maintain high levels of testosterone within the seminiferous tubules, supporting spermatogenesis.

5. Feedback Regulation:

   • FSH secretion is regulated by feedback mechanisms involving gonadal hormones (e.g., estrogen, inhibin) and hypothalamic hormones (e.g., gonadotropin-releasing hormone, GnRH).
   • Elevated levels of estrogen and inhibin in females and testosterone in males exert negative feedback on the anterior pituitary and hypothalamus, inhibiting further FSH release.

In summary, FSH plays a crucial role in regulating reproductive function by promoting follicle development and estrogen production in females and supporting spermatogenesis in males. Its actions are mediated through specific cell surface receptors and intracellular signaling pathways, ultimately leading to the maturation of ovarian follicles and the production of mature sperm cells.